1. Technical Field
The present invention relates to toner particle-bearing rollers, developing devices and image forming apparatuses.
2. Related Art
Image forming apparatuses such as laser beam printers are well known. Such image forming apparatuses include, for example, an image-bearing member for bearing a latent image, and a developing device for developing the latent image borne by the image-bearing member with toner particles. When an image signal or the like is sent from an external device, such as a host computer, to such an image forming apparatus, the developing device is positioned at the developing position opposite the image-bearing member, a toner image is formed by developing the latent image borne by the image-bearing member with toner particles inside the developing device, and an image is ultimately formed on the medium by transferring this toner image onto the medium.
This developing device includes a toner particle-bearing roller, which bears toner particles on its surface and develops a latent image borne by the image-bearing member with the toner particles, in order to achieve the above-described function of developing the latent image borne by the image-bearing member.
Moreover, the developing devices are known in which projection portions are formed in the surface of the toner particle-bearing roller, in order to suitably bear the toner particles. However, if the surface of the toner particle-bearing roller is provided with projection portions, then forces may act locally from the projection portions on the toner particles, depending on the shape of the projection portions. For example, if the projection portions are sharp, then the forces from the projection portions may concentrate locally on the toner particles when the projection portions contact the toner particles. Thus, when the forces from the projection portions concentrate locally on the toner particles, these forces may cause a deformation of the toner particles and there is the risk that the toner particles may break.
Moreover, in order to suitably bear toner particles, the surface of the toner particle-bearing roller may be prbvided with depression portions having a flat bottom surface and lateral surfaces adjacent to that bottom surface. In this case, there is a risk that toner particles, especially finely particulate toner particles, accumulate at the boundaries between the bottom surface and the lateral surfaces.
Furthermore, toner particle-bearing rollers are known whose surface is provided with depression portions and projection portions that are arranged regularly. The developing of the latent image borne by the image-bearing member with toner particles that are borne on the surface of the toner particle-bearing roller is executed in a state in which the toner particle-bearing roller is in opposition to the image-bearing member, and at that time, a situation may occur in which the distance between the toner particles borne in the depression portions of the toner particle-bearing roller and the latent image borne by the image-bearing member is larger than the distance between the toner particles borne by the projection portions and the latent image. In this situation, the density of the toner image formed on the image-bearing member by the toner particles borne in the depression portions becomes lower than the density of the toner image formed on the image-bearing member by the toner particles borne in the projection portions, and there is the risk of density unevenness occurring in the toner image.
It should be noted that JP-A-2003-263018, JP-A-1-102486, and JP-A-5-142950 are examples of related technology.